Image intensifier devices are employed in night visions systems to convert a dark environment to a bright environment that is perceivable by a viewer. Night vision systems have industrial, commercial and military applications. The image intensifier device collects tiny amounts of light in a dark environment, including the lower portion of the infrared light spectrum, that are present in the environment but imperceptible to the human eye. The device amplifies the light so that the human eye can perceive the image. The light output from the image intensifier device can either be supplied to a camera, external monitor or directly to the eyes of a viewer.
Image intensifier devices generally include three basic components mounted within an evacuated housing, namely, a photocathode (commonly called a cathode), a microchannel plate (MCP) and an anode. The photocathode is a photosensitive plate capable of releasing electrons when it is illuminated by light. The MCP is a thin glass plate having an array of channels extending between one side (input) and another side (output) of the glass plate. The MCP is positioned between the photocathode and the anode.
The outer surfaces of the MCP may be coated with an ion barrier film. Coating the exterior surfaces of the MCP with a thin film achieves an appreciable improvement in the performance and service life of the image intensifier tube, as compared with filmless MCP's. Incorporating a filmed MCP into an image intensifier tube has generated a new set of challenges. Solutions to meet those challenges are described herein.
In operation, an incoming electron from the photocathode enters the input side of the MCP and strikes a channel wall. When voltage is applied across the MCP, the incoming or primary electrons are amplified, generating secondary electrons. The secondary electrons exit the channel at the output side of the MCP. The secondary electrons exiting the MCP channel are negatively charged and are therefore, attracted to the positively charged anode. The anode may be a phosphor screen, or a silicon imager such as a complementary metal oxide semiconductor (CMOS) or a charged coupled device (CCD), for example.
The three basic components of the image intensifier device are positioned within an evacuated housing or vacuum envelope. The vacuum facilitates the flow of electrons from the photocathode through the MCP and to the anode. A non-evaporable getter is positioned in the evacuated housing for maintaining the vacuum condition by collecting gas molecules. Non-evaporable getter devices, which are well known in the art, are used to exhaust unwanted gases from evacuated electron tubes. The use of getter materials is based on the ability of certain solids to collect free gases by adsorption, absorption or occlusion, as is well known in the art. Promoting and maintaining vacuum within the image intensifier device housing is a goal of image intensifier device manufacturers. With that goal in mind, the image intensifier device described herein maximizes the use of getter material and incorporates sealing structures in the interest of maintaining a vacuum condition within the housing.
There is a continuing need to further develop and refine the components of image intensifier devices and methods for assembling image intensifier devices in the interest of performance, reliability, manufacturability, cost and ease of assembly.
The following U.S. patents are incorporated by reference herein in their entirety: U.S. Pat. No. 5,493,111 to Wheeler et al., U.S. Pat. No. 6,586,877 to Suyama et al., U.S. Pat. No. 6,040,657 to Vrescak et al., U.S. Pat. No. 6,747,258 to Benz et al., U.S. Pat. No. 6,331,753 to Iosue, U.S. Pat. No. 4,039,877 to Wimmer, U.S. Pat. No. 5,510,673 to Wodecki et al., U.S. Pat. No. 6,483,231 to Iosue, U.S. Pat. No. 5,994,824 to Thomas, U.S. Pat. No. 6,847,027 to Iosue, and U.S. Pat. No. 5,994,824 to Thomas. The following U.S. patent applications are incorporated by reference herein in their entirety: Ser. No. 11/193,065 to Costello, Ser. No. 11/194,865 to Thomas, Ser. No. 10/482,767 to Yamauchi et al. and Ser. No. 10/973,336 to Shimoi et al.